The 13th Hintze Biannual Lecture delivered by Professor David Spergel Observations of the microwave background, the left-over heat from the big bang, the large-scale distribution of galaxies and the properties of distant supernova have led to a remarkable simple model for our universe. With only five parameters (the density of atoms, the density of matter,

the age of the universe, the amplitude of fluctuations in the early universe and their scale dependance), this model can fit a host of astronomical observations. We have now determined these basic parameters at the few percent level or better. While simple, our universe is very strange. Atoms make up only 5% of the universe, most of the universe is made of mysterious dark matter and dark energy. We do not understand how the universe began or why there is more matter than anti-matter. I will review our current understanding and look forward to future measurements that can address these big open questions.